This invention relates to a droplets jetting device in which a progressive wave of a Rayleigh mode elastic surface wave is utilized to splash a liquid in the form of droplets from the propagation surface thereof.
In a conventional droplet jetting device, the bulk wave of a piezo-electric element is used to apply alternate pressure to the liquid in a closed container thereby to jet liquid in the form of droplets through a small nozzle connected to the container.
One example of the conventional droplets jetting device will be described with reference to FIG. 5. In FIG. 5, reference numeral 11 designates a liquid to be jetted in the form of droplets; 12, a container in which the liquid is put, namely, a pressure chamber; 13, a cylindrical piezo-electric element for applying pressure to the liquid; 14, a nozzle for jetting the liquid in the form of droplets; 15, a fluid resistance element for limiting the flow of the liquid; 16, a valve for allowing the liquid to flow only towards the nozzle; and 17, a liquid supplying path.
A voltage is applied across the electrodes formed on the inner and outer walls of the cylindrical piezo-electric element 13 so that the latter 13 is contracted radially. As a result, the liquid 11 in the pressure chamber 12 is pressurized, so that it is passed through the fluid resistance element 15 and jetted from the nozzle 14. As the quantity of liquid in the pressure chamber decreases in this manner, the liquid is supplied thereinto through the liquid supply path 17. As is apparent from the above description, the liquid is jetted in the form of droplets from the nozzle 14 successively by applying an AC voltage to the piezo-electric element 13.
The conventional device employs the nozzle to form droplets as required. In order to reduce the size of droplets, it is necessary to decrease the diameter of the nozzle. To manufacture such a small diameter nozzle is rather difficult. In the case where the liquid is ink, the device suffers from the following difficulties: When the ink dries, the nozzle becomes clogged; therefore, the maintenance of the device is troublesome, and reliability of the device decreases. Those difficulties may be eliminated by adding an ink drying preventing mechanism or a nozzle cleaning mechanism to the device. However, the addition of such a mechanism may result in other difficulties such that the device becomes more intricate in construction, larger in size, and higher in manufacturing cost.